1. Field of Invention
The present invention generally relates to a method and composition for the detection of bacteria. More particularly, the invention relates a method and composition for the rapid detection of mycobacteria.
2. Description of Related Art
Tuberculosis continues to be a major health problem around the world. It is estimated that every year ten million people become tuberculosis patients and three million die of this disease. Definitive diagnosis of tuberculosis typically requires isolation of Mycobacterium tuberculosis, or other species of mycobacteria that may cause similar diseases, from patients' clinical samples grown in microbiological culture media. Obtaining pathogenic mycobacteria as pure culture is also important in determining its susceptibility to antituberculosis drugs.
In conventional mycobacterial culture media, the growth of mycobacteria is detected by visualization of colonies formed by mycobacteria, which generally requires 3 to 8 weeks. To shorten the duration of time required for growth detection, several rapid mycobacterial culture systems using Middlebrook liquid medium have been developed. These systems have disadvantages, however, such as using radioactive substances, requiring expensive equipment and/or having difficulties in application.
One of the oldest and most widely used rapid detection systems is the radiometric culture system in which mycobacterial growth is monitored by the formation of radioactive CO2 from 14C labeled palmitic acid included in the Middlebrook media. This method has the major disadvantage of using radioactive chemicals that requires the disposal of culture bottles using special precautions.
More recently, a fluorometric system has been developed in which mycobacterial growth is monitored by a decrease in oxygen and formation of CO2 that reduces an indicator embedded in a gel at the bottom of the tube. Reduction of the indicator causes the indicator to fluoresce when activated by UV light. The culture tubes may be evaluated either visually using a UV light source or by an automated instrument.
In another system carbon dioxide released into liquid Middlebrook medium by actively growing mycobacteria is detected through a colorimetric indicator embedded in a gel at the bottom of culture vials. Color changes are monitored by a reflectometric detection unit.
Another system is based on detection of pressure changes resulting from gas production or gas consumption in the headspace of the culture bottle. Although the growth detection principles, in the rapid culture systems described above, are different, they all contain modified types of Middlebrook medium in culture vials. With these systems, it is not possible to differentiate mycobacterial growth from contamination without doing microscopy or further tests.